Effect of self-association of phenol on its transport across polyethylene film.

Phenol diffusion across a high density polyethylene film from isooctane, in which phenol self-associates, demonstrated nonideal behavior. The steady-state flux of phenol across the film was not directly proportional to its concentration in the donor phase. At higher donor phase concentrations, negative steady-state flux deviations were observed. These negative deviations were due to phenol self-association in the donor phase and the resulting decreases in thermodynamic activity. By using a monomer--pentamer model for phenol self-association in isooctane, the steady-state flux was shown to be directly proportional to the phenol monomer concentration in the donor phase. Although steady-state flux concentration deviations were observed, the diffusion time lag was independent of the permeant concentration and reflected the intrinsic diffusivity of the film to phenol.